Answer:
11.45kcal/g
2.612 × 10³ kcal
Explanation:
When a compound burns (combustion) it produces carbon dioxide and water. The combustion of 2-methylheptane can be represented by the following balanced equation:
2 C₈H₁₈ + 25 O₂ ⇄ 16 CO₂ + 18 H₂O
It releases 1.306 × 10³ kcal every 1 mol of C₈H₁₈ that is burned.
<em>What is the heat of combustion for 2-methylheptane in kcal/gram?</em>
We know that the molar mass of C₈H₁₈ is 114.0g/mol. Then, using proportions:

<em>How much heat will be given off if molar quantities of 2-methylheptane react according to the following equation? 2 C₈H₁₈ + 25 O₂ ⇄ 16 CO₂ + 18 H₂O</em>
In this equation we have 2 moles of C₈H₁₈. So,

oxygen and silicon I believe
The empirical formula CH₂ has a mass [(12 × 1) + (1 × 2)] = 14 g/mol
If the empirical formula is 14 g/mol,
and the molecular formula is ~140 g/mol
Then the multiple is = 140 g/mol ÷ 14 g/mol
= 10
Therefor the molecular formula is 10(CH₂) = <span>C</span>₁₀<span>H</span>₂₀<span> </span>